diff --git a/mac/lib/machine_id_mac.cc b/mac/lib/machine_id_mac.cc
index 7515eb9..3a708c3 100644
--- a/mac/lib/machine_id_mac.cc
+++ b/mac/lib/machine_id_mac.cc
@@ -2,13 +2,145 @@
 // Use of this source code is governed by an Apache-style license that can be
 // found in the COPYING file.
 
+#include <CoreFoundation/CoreFoundation.h>
+#include <IOKit/IOKitLib.h>
+#include <IOKit/network/IOEthernetInterface.h>
+#include <IOKit/network/IONetworkInterface.h>
+#include <IOKit/network/IOEthernetController.h>
+
 #include "base/logging.h"
+#include "base/mac/foundation_util.h"
+#include "base/mac/scoped_cftyperef.h"
+#include "base/mac/scoped_ioobject.h"
 #include "base/string16.h"
+#include "base/stringprintf.h"
+#include "base/sys_string_conversions.h"
+#include "base/utf_string_conversions.h"
 
 namespace rlz_lib {
 
+namespace {
+
+// See http://developer.apple.com/library/mac/#technotes/tn1103/_index.html
+
+// The caller is responsible for freeing |matching_services|.
+bool FindEthernetInterfaces(io_iterator_t* matching_services) {
+  base::mac::ScopedCFTypeRef<CFMutableDictionaryRef> matching_dict(
+      IOServiceMatching(kIOEthernetInterfaceClass));
+  if (!matching_dict)
+    return false;
+
+  base::mac::ScopedCFTypeRef<CFMutableDictionaryRef> primary_interface(
+      CFDictionaryCreateMutable(kCFAllocatorDefault, 0,
+                                &kCFTypeDictionaryKeyCallBacks,
+                                &kCFTypeDictionaryValueCallBacks));
+  if (!primary_interface)
+    return false;
+
+  CFDictionarySetValue(
+      primary_interface, CFSTR(kIOPrimaryInterface), kCFBooleanTrue);
+  CFDictionarySetValue(
+      matching_dict, CFSTR(kIOPropertyMatchKey), primary_interface);
+
+  kern_return_t kern_result = IOServiceGetMatchingServices(
+      kIOMasterPortDefault, matching_dict.release(), matching_services);
+
+  return kern_result == KERN_SUCCESS;
+}
+
+bool GetMACAddressFromIterator(io_iterator_t primary_interface_iterator,
+                               uint8_t* buffer, size_t buffer_size) {
+  if (buffer_size < kIOEthernetAddressSize)
+    return false;
+
+  bool success = false;
+
+  bzero(buffer, buffer_size);
+  base::mac::ScopedIOObject<io_object_t> primary_interface;
+  while (primary_interface.reset(IOIteratorNext(primary_interface_iterator)),
+         primary_interface) {
+    io_object_t primary_interface_parent;
+    kern_return_t kern_result = IORegistryEntryGetParentEntry(
+        primary_interface, kIOServicePlane, &primary_interface_parent);
+    base::mac::ScopedIOObject<io_object_t> primary_interface_parent_deleter(
+        primary_interface_parent);
+    success = kern_result == KERN_SUCCESS;
+
+    if (!success)
+      continue;
+
+    base::mac::ScopedCFTypeRef<CFTypeRef> mac_data(
+        IORegistryEntryCreateCFProperty(primary_interface_parent,
+                                        CFSTR(kIOMACAddress),
+                                        kCFAllocatorDefault,
+                                        0));
+    CFDataRef mac_data_data = base::mac::CFCast<CFDataRef>(mac_data);
+    if (mac_data_data) {
+      CFDataGetBytes(
+          mac_data_data, CFRangeMake(0, kIOEthernetAddressSize), buffer);
+    }
+  }
+
+  return success;
+}
+
+bool GetMacAddress(unsigned char* buffer, size_t size) {
+  io_iterator_t primary_interface_iterator;
+  if (!FindEthernetInterfaces(&primary_interface_iterator))
+    return false;
+  bool result = GetMACAddressFromIterator(
+      primary_interface_iterator, buffer, size);
+  IOObjectRelease(primary_interface_iterator);
+  return result;
+}
+
+CFStringRef CopySerialNumber() {
+  base::mac::ScopedIOObject<io_service_t> expert_device(
+      IOServiceGetMatchingService(kIOMasterPortDefault,
+          IOServiceMatching("IOPlatformExpertDevice")));
+  if (!expert_device)
+    return NULL;
+
+  base::mac::ScopedCFTypeRef<CFTypeRef> serial_number(
+      IORegistryEntryCreateCFProperty(expert_device,
+                                      CFSTR(kIOPlatformSerialNumberKey),
+                                      kCFAllocatorDefault,
+                                      0));
+  CFStringRef serial_number_cfstring =
+      base::mac::CFCast<CFStringRef>(serial_number);
+  if (!serial_number_cfstring)
+    return NULL;
+
+  ignore_result(serial_number.release());
+  return serial_number_cfstring;
+}
+
+}  // namespace
+
 bool GetRawMachineId(string16* data, int* more_data) {
-  NOTIMPLEMENTED();
+  uint8_t mac_address[kIOEthernetAddressSize];
+
+  data->clear();
+  if (GetMacAddress(mac_address, sizeof(mac_address))) {
+    *data += ASCIIToUTF16(StringPrintf("mac:%02x%02x%02x%02x%02x%02x",
+        mac_address[0], mac_address[1], mac_address[2],
+        mac_address[3], mac_address[4], mac_address[5]));
+  }
+
+  // A MAC address is enough to uniquely identify a machine, but it's only 6
+  // bytes, 3 of which are manufacturer-determined. To make brute-forcing the
+  // SHA1 of this harder, also append the system's serial number.
+  CFStringRef serial = CopySerialNumber();
+  if (serial) {
+    if (!data->empty())
+      *data += UTF8ToUTF16(" ");
+    *data += UTF8ToUTF16("serial:") + base::SysCFStringRefToUTF16(serial);
+    CFRelease(serial);
+  }
+
+  // On windows, this is set to the volume id. Since it's not scrambled before
+  // being sent, just set it to 1.
+  *more_data = 1;
   return true;
 }